1. Field of the Invention
This invention relates to a process for preparing a spandex supply package intended for passive feeding of the spandex to various types of textile equipment and, more specifically, to a process that results in a package that permits improved uniformity of feeding of the spandex.
2. Description of Background Art
Spandex is well known and widely used in the manufacture of knitwear. "Spandex" is a manufactured fiber or filament in which the fiber-forming substance is a long chain synthetic elastomer comprised of at least 85% by weight of a segmented polyurethane. After dry-spinning, spandex is wound on a package (also known as a cake or bobbin) at a predetermined tension. The tension causes the spandex to be in an extended state in the package. The percent package relaxation value, %R, of any segment of the spandex wound in the supply package is a measure of the extension of the spandex in that segment and is defined by equation (I): EQU %R=100.times.[(L.sub.s -L.sub.r)/L.sub.s ] (I)
where in any segment of yarn unwound (i.e., removed) from the package, L.sub.r is the relaxed length of the unwound segment, and L.sub.s is the stretched length which the unwound segment had while still wound and under tension in the supply package. %R, L.sub.r, and L.sub.s, are determined by the "package relaxation value" test described hereinafter. As used herein, "segment" refers to a selected fraction of the length of the spandex in a package.
A spandex supply package is conventionally wound up at a constant windup speed from the start to the end of the winding of the package. As a result of the constant windup speed, the spandex in the package has percent package relaxation values that vary from a large value in the outside layer of the package to a smaller value in the middle layer of the package and then to a larger value again in the inner layer nearest the core of the package. This variation in percent package relaxation can cause uniformity problems in downstream processing.
When fabrics are knit with spandex, the spandex is forwarded from a supply package to a knitting machine by means of an active or a passive feeding device. An active feeding device removes the spandex from the package while the package is rotated by a surface-contacting driven roller or by driven rotation of the tube on which the spandex is wound. A passive feeding device removes the spandex from the supply package by pulling the spandex over one end of the supply package (i.e., "over-end take-off") or by pulling the spandex tangentially from the surface of the supply package while the package is free to rotate on its tubular axis. Passive feeding devices are more economical than active feeding devices. However, when a conventionally prepared spandex supply package is used with a passive feeding device, nonuniform unwinding is often encountered, due to nonuniform package relaxation. In knitting operations, the nonuniform unwinding can cause uneven knitting, variations in fabric size (i.e., dimensions) and fabric of low quality.
A conventional method for decreasing the problems associated with non-uniform unwinding of spandex yarns with passive feeding devices, is disclosed, for example, in Japanese Patents Kokai Sho 51-127229, Kokoku Sho 62-21714, and Kokai Hei 1-226669. In such a method, cylindrical supply packages which were formed by winding up spandex at a constant speed on a tubular core as the spandex emerged from a dry spinning process are completely rewound to form a new package. The rewound spandex supply packages have less tackiness and fewer nonuniformities in subsequent knitting operations. However, rewinding spandex supply packages is time-consuming, labor intensive and expensive. Furthermore, even when such a rewound package is used with passive feeding device, undesirable thread breaks and knit fabric non-uniformities are still encountered, although at a somewhat lower frequency than with conventional spandex supply packages that were not rewound.
U.S. Pat. No. 4,615,495 to Correll discloses low density, substantially cylindrical, wound packages of substantially tensionless elastic yarn prepared by rewinding yarn (a feed yarn) from an existing package of yarn. Correll eliminates friction from the yarn, thereby maintaining a constant velocity of the yarn after leaving the overfeed rolls to obtain a tensionless wound package, by transforming the yarn guide portion of a traverse mechanism into a fluid jet. Such a tensionless package, however, is not stable.
In view of the above-described problems with spandex supply packages, there is a need to provide a process for making an improved spandex supply package that requires no rewinding and provides acceptable passive feeding characteristics.